William Thornton Kemper Sr. (November 2, 1867 – January 19, 1938) was an American banker who was the patriarch of the Missouri Kemper family, which developed both Commerce Bancshares and United Missouri Bank to become a major banking family in the Midwest.

At the age of 14 he began work, sweeping the floor at Collins and White, a St. Joseph shoe store, and later became a salesman for Noyes, Norman and Company, a shoe distributor and manufacturer (also in St. Joseph) in which his father was a part owner, covering retailers in eastern Kansas, including Valley Falls, Kansas.

Kemper would spend the next eight years in Valley Falls, where he courted and married Charlotte Crosby and began a career in commercial banking.

In the years following the Civil War, such towns were promoted as commercial hubs in the new network of regional and trans-continental railroads.

Kemper's connection with the Crosby family had both business and personal aspects, and may have predated his move to Valley Falls.

An outspoken Abolitionist, Crosby was a signer of the first Kansas State Constitution; he commanded a local free-state volunteer militia; his first store in Valley Falls was burned to the ground in 1856 by Border Ruffians (pro-slavery guerrilla fighters).

In 1879, Crosby started the Valley Falls Bank of Deposit, selling his interest in the store to his partner and brother-in-law, Alvin Kendall.

In 1902, he established the Kemper Loan and Investment Company, which had a very broad charter to finance and trade securities and real estate.

[11] James M. Kemper joined Commerce Trust as treasurer in 1924; he led Commerce Trust from 1925 to 1964, succeeded by his son, James Kemper Jr.[12] In 1917, Kemper was appointed receiver for the bankrupt assets of the Kansas City, Mexico & Orient Railroad, a railroad system conceived and promoted by Arthur Stillwell in 1900 to link Kansas City by rail to the Pacific ocean port of Topolobampo on the west coast of Mexico, but which was never fully completed.

However, in March 1924 the U.S. Government ordered that the Orient be sold at auction to satisfy previous loans and accrued interest.

Kemper and Clifford Histed were successful bidders in that auction, with a bid of $3 million (which was approximately the amount of government debt).

John took Harry, then a teenager, to the local Democratic functions in Kansas City where Kemper was also in attendance.